The present invention relates to a radiation sensitive resin composition, an insulating film made therefrom and an organic EL display element comprising the insulating film. More specifically, it relates to a positive type radiation sensitive resin composition suitable for the formation of an insulating film using radiation such as ultraviolet ray, deep ultraviolet ray, X-ray, electron beam, molecular beam, xcex3-ray, synchrotron radiation or proton beam, an insulating film made therefrom and an organic EL display element comprising the insulating film.
Compared with liquid crystal display elements, organic EL elements have various advantages such as no dependence upon view angle as they emit light themselves, as well as excellent impact resistance, low voltage drive, low power consumption and high operational stability at low temperatures as they are solid elements. Passive type organic EL elements have the advantage of low cost since they are simple matrix elements. Owing to these advantages, the organic EL elements are highly expected to be used for mobile applications such as portable terminals and car equipment, and active studies on these organic EL elements are now under way.
The production of the above organic EL elements is generally carried out by the following method. A transparent electrode (hole injection electrode) made from, for example, tin doped indium oxide (ITO) and a hole transport layer pattern are formed on a substrate. In the case of a passive type organic EL element, after an insulating film pattern and a cathode partition pattern are formed, organic EL layer, electron transport layer and cathode are patterned by deposition. In the case of an active type organic EL element, after an ITO pattern and a hole transport layer pattern are formed, an insulating layer pattern which will become partitions for the organic EL layer is formed, followed by the formation of an organic EL layer pattern by a masking method and the formation of electron transport layer and cathode patterns.
The organic EL layer is generally made from a material formed by doping a base material such as Alq3 or BeBq3 with quinacridone or coumarin and the cathode is generally made from a material essentially composed of a metal having a low work function such as Mg or Ag.
The insulating film material is generally an acrylic material having alkali developability or a polyimide material having organic developability. However, the following problem is encountered in this case.
The hole transport layer, organic EL layer and electron transport layer are often made from a basic material such as an amine-based material to suitably transport holes or electrons. However, this material readily undergoes a structural change due to a trace amount of water and deterioration by an organic substance. Therefore, when the water permeability of an insulating film material is large or the residue after development exists at the time of forming an insulating film pattern, a phenomenon such as the spread of a non-emitting portion (dark area) occurs. Since a cathode essentially composed of a metal having a low work function is readily oxidized, a similar problem arises.
Particularly in the case of a passive type organic EL element, a portion made from the basic material is in direct contact with an insulating film. As this insulating film must have alkali developability or organic developability, it shows the acidity of carboxylic acid or phenol and reacts with the above basic material through water on the contact surface, or water changes the structure of the insulating film directly. When the water permeability of the insulating film is large, the insulating film promotes corrosion by an acid. A cathode essentially composed of a metal having a low work function is corroded through its reaction with an acid, thereby forming a dark spot (non-luminous spot).
When the angle (tapered angle) formed by the bottom side and the tangent of the edge portion of the sectional form of the formed insulating film is large, an organic EL layer formed by deposition may crack, whereby water enters from the crack to cause an emission failure.
Further, an insulating film made from a conventionally known material does not have sufficient resistance to a resist remover which is used to form a cathode for a passive type organic EL element, thereby making it impossible to produce an organic EL display element stably.
An insulating film material which can solve the above problems has not been proposed yet and it has been impossible to produce an organic EL element having sufficiently long service life stably.
Meanwhile, an organic EL display element having a high aperture for high definition is now under study. This organic EL element is produced by the following method, for example.
A drive terminal is formed on a substrate such as a glass substrate and an insulating film having flattening performance is formed on the terminal. A transparent electrode (hole injection electrode) pattern made from ITO, for example, is formed on the insulating film. The pattern is generally formed by wet etching.
A hole transport layer, organic EL layer, electron transport layer and electron injection electrode are then formed on the pattern sequentially.
A 1 to 15 xcexcm through hole or a U-shaped cavity must be formed in the insulating film used in the organic EL display element having the above structure to communicate the ITO electrode (hole injection electrode) formed above the insulating film with the drive terminal below the insulating film. The insulating film must have excellent flattening performance, high transparency and high resistance to a resist remover.
However, a material capable of forming an insulating film having such high resolution that the above through hole or U-shaped cavity can be formed therein, excellent flattening performance, high transparency and high resistance to a resist remover has not been proposed yet.
It is an object of the present invention to provide a radiation sensitive resin composition for forming an insulating film which enables the stable production of an organic EL element having long service life.
It is another object of the present invention to provide a radiation sensitive resin composition for forming an insulating film which enables the formation of a through hole or U-shaped cavity therein and has excellent flattening performance, high transparency and high resistance to a resist remover.
It is still another object of the present invention to provide an insulating film formed from the above radiation sensitive resin composition.
It is a further object of the present invention to provide an organic EL element comprising the above insulating film.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a radiation sensitive resin composition (may be referred to as xe2x80x9cfirst compositionxe2x80x9d hereinafter), comprising:
(1) (a) an alkali-soluble resin having no epoxy group, and (b) a 1,2-quinonediazide compound, and (2) being for forming an insulating film for an organic EL display element.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a radiation sensitive resin composition, comprising:
(1) (axe2x80x2) an alkali-soluble resin having an epoxy group, and (b) a 1,2-quinonediazide compound, and (2) being for forming an insulating film for an organic EL display element.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by an insulating film for an organic EL display element, which is formed from the above first composition or the above second composition of the present invention.
According to the present invention, fourthly, the above objects and advantages of the present invention are attained by an organic EL display element comprising an insulating film formed from the above first composition or the above second composition of the present invention.